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I plan to image the sun with a white light filter. Would It help to use an IR cut filter or an IR pass filter? Is it true that IR pass is more cloud resistant? Thanks! |
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| Mostly if not always, white light filter = no IR. And you don't want it any other way. And there is no such a thing as "cloud-resistant" band-pass. |
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| So I should have no other filter? Only white light? |
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| You can put any other filter, Ha for example or double-stack continuum filter. Just after the white light filter. |
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| I use a deep R filter. |
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Such a simple question but so many "well it depends" answers! You should be able to use most WL filters without any additional filtering. Certainly for visual. But for imaging it depends on how sensitive your camera is to IR. No harm using a UV/IR cut filter. If your sensor has high IR sensitivity it can help reduce IR "bloom" or haziness. I always have one somewhere when I'm imaging solar. They're cheap, keeps dust out of things, stops other elements getting scratched. You'd use an IR pass if you only wanted to image infrared. It only passes infrared. Not what you want. If you have a mono cam then adding a colour filter (red/green/blue) can help give sunspots a contrast boost. I'd go for green or red. Once you go the blue end you get into complexities regarding aperture/seeing/sampling. If you have a colour cam then those built in RGB filter dots over the tiny pixels may help filter out IR anyway. To improve surface detail contrast I'd use a green filter, because colour cams have more green dots compared to red or blue. You get more resolution from the green channel. Manufacturers do this because the human eye is more sensitive to green, so colour imaging chips are biased to human expectations. Using a Baader WL filter on my Celestron C9.25 I can see straw/amber colours around sunspots - and I promise it's not chromatic aberrations! But to image (with mono cam) I get much better surface detail using a "continuum" filter (greenish) or red (actually 7nm Ha but essentially red). I've always used Baader "Astro Solar" film. It's not the cheapest but it's still cheap, considering it stops your telescope and camera bursting into flames. "White light" contains "all the frequencies". Here's a transmission plot of Baader film:  Full article: https://www.researchgate.net/figure/Transmittance-spectra-of-solar-filters-blue-the-Baader-AstroSolar-Photo-Film-ND-M38_fig3_230738698 Baader film does allow IR+. The solar glasses they sell though are 100% "CE-certified EN ISO 12312-2:2015" More info here: Differences in AstroSolar® Solar Films |
